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A paleontological deposit near San Clemente de Térapa represents one of the very few Rancholabrean North American Land Mammal Age sites within Sonora, Mexico. During that time, grasslands were common, and the climate included cooler and drier summers and wetter winters than currently experienced in northern Mexico. Here, we demonstrate restructuring in the mammalian community associated with environmental change over the past 40,000 years at Térapa. The fossil community has a similar number of carnivores and herbivores whereas the modern community consists mostly of carnivores. There was also a 97% decrease in mean body size (from 289 kg to 9 kg) because of the loss of megafauna. We further provide an updated review of ungulates and carnivores, recognizing two distinct morphotypes of Equus, including E. scotti and a slighter species; as well as Platygonus compressus; Camelops hesternus; Canis dirus; and Lynx rufus; and the first regional records of Palaeolama mirifica, Procyon lotor, and Smilodon cf. S. fatalis. The Térapa mammals presented here provide a more comprehensive understanding of the faunal community restructuring that occurred in northern Mexico from the late Pleistocene to present day, indicating further potential biodiversity loss with continued warming and drying of the region.

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Yes / The mechanisms regulating community composition and local dominance of trees in species-rich forests are poorly resolved, but the importance of interactions with soil microbes is increasingly acknowledged. Here, we show that tree seedlings that interact via root-associated fungal hyphae with soils beneath neighbouring adult trees grow faster and have greater survival than seedlings that are isolated from external fungal mycelia, but these effects are observed for species possessing ectomycorrhizas (ECM) and not arbuscular mycorrhizal (AM) fungi. Moreover, survival of naturally-regenerating AM seedlings over ten years is negatively related to the density of surrounding conspecific plants, while survival of ECM tree seedlings displays positive density dependence over this interval, and AM seedling roots contain greater abundance of pathogenic fungi than roots of ECM seedlings. Our findings show that neighbourhood interactions mediated by beneficial and pathogenic soil fungi regulate plant demography and community structure in hyperdiverse forests. / This research was funded by the National Key Research and Development Program of China (Project No. 2017YFA0605100) and the National Natural Science Foundation of China (NSFC 31770466 to X.L. and 31870403 to M.L.), and partly supported by awards from the UK Natural Environment Research Council (NERC NE/M004848/1 and NE/R004986/1). D.J. is also supported by the N8 AgriFood programme.

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<p><a>Natural enemy ecology strives to integrate the fields of disease ecology and community ecology to forge a broader understanding of how pathogens and predators structure communities. To advance this field, we need a greater emphasis on: 1) quantifying pathogen-mediated effects on community structure and comparing these effects to those observed with predators and 2) determining the interactive effects of combined natural enemies on communities. I conducted a mesocosm experiment designed to assess the individual and combined effects of predators (dragonfly larvae and adult water bugs) and a pathogen (ranavirus) on a larval amphibian community. Additionally, I conducted laboratory experiments to assess whether ranavirus exposure increases the vulnerability of tadpoles to predation. In my laboratory experiments, I found that virus exposure increased predation rates with dragonflies, but not water bugs. For tadpoles in the dragonfly treatments, the probability of survival for virus-exposed tadpoles was 66-77% lower compared to unexposed tadpoles. This data suggests that predators may selectively remove infected individuals from the population, which can enhance the magnitude of the healthy herds effect. I found that the risk level of the predators largely explained effects on the community. For instance, high-risk dragonflies reduce overall survival to 30% whereas low-risk water bugs only reduced survival to 67%. Additionally, I found that virus reduce survival to 62%, which was comparable to effect of the low-risk predator. Interestingly, all three natural enemies influenced community structure (i.e. species relative abundance) in unique ways. These results demonstrate that pathogens can have effects similar to predators on communities, and that natural enemy identity is important when considering impacts on community structure. When predators were combined with the virus, I found that mortality was relatively unchanged from the predator-only treatments suggesting less than additive effects of combined natural enemies. This result was driven by the healthy herds effect; the presence of dragonflies reduced overall infection prevalence in the community to 7% compared to 30% in the virus-only treatment. This effect was observed in the water bug treatments, to a lesser degree, suggesting that predator risk or efficiency contributes the magnitude of the effect. Collectively, my work demonstrates the importance of examining the individual and combined effects of natural enemies on ecological communities.</a></p>

The western Amazon is known to be one of the most biologically diverse regions in the world, yet information about the spatial distribution of that biodiversity and the processes governing its distribution remains scarce. An improved understanding of those biogeographic patterns and processes can inform conservation and development planning in areas where anthropogenic landscape change is ongoing. Spatial components of biodiversity are known to be influenced by historical and present-day physical and human geographic processes. There is evidence that major Amazonian rivers form the boundaries of biological regions, at least for birds. Other factors that may influence bird species composition include the dispersal limitations of individual species, forest plant species composition and structure, topography, forest fragmentation, and hunting. Sites where bird species composition was measured in this study represented mature, upland forest on both sides of the Amazon River, and a range of non-flooded forest types, as indicated by soil and plant surveys. Bird species compositional variation was closely correlated with variation in plant species composition, human disturbance associated with forest fragmentation, and position north or south of the Amazon River. The strongest differences were between opposite sides of the river, even though local environments, including plant composition, were not different on the two sides. This strongly suggests that historical biogeographic factors, rather than present-day environmental gradients, are responsible for bioregional boundaries at Amazonian rivers. The difference between plant and bird distributions at this scale underscores the pressing need to re-evaluate general notions of bioregional complexity and pattern in the Amazon basin. Locally, the influence of habitat fragmentation on animal communities, including reduced species richness, was confirmed. The influence of local floristic variation is of particular importance due to its ubiquity across western Amazonia. Thus, understanding the distributions of soils and vegetation is critical for explaining Amazonian animal diversity. The use of these factors to model bird community heterogeneity contradicts assumptions that the processes shaping Amazonian animal community diversity are too complex to measure efficiently, and their use contributes a new understanding of the dimensions of that diversity. / text

Diversity within a habitat is determined largely by ecology and species interactions. Studies to date, however, rarely examined the role of intraspecific aggression in promoting coexistence and diversity. This is especially true in cities, where community ecology is poorly understood. This knowledge is important for basic understanding of how ecological principals come into play in our newly created habitats, as well as for reconciling human-dominated areas for wildlife.I studied the effect of human-made habitats on hummingbird abundance and diversity in Tucson, Arizona. To do that, I examined community organization and competitive interactions among four hummingbird species. I answer the questions: What is the community organization of hummingbirds in Tucson? How do characteristics of human habitats (e.g., landscaping and artificial resources) affect diversity? What mechanism underlies this pattern? And how can we apply this knowledge to conservation?To perform this study, I established a citizen science project - the Tucson Hummingbird Project (http://hummingbirds.arizona.edu). Trained participants reported abundance and behavior of hummingbirds in their backyards. Landscaping and resources (feeders and nectar plants) varied between yards.Results show that the distribution of hummingbirds in Tucson varies by species. Diversity, rather than merely abundance, increased with higher habitat heterogeneity and with more resources. Competitive interactions differ between species. Notably, intraspecific competition takes precedence over interspecific competition in the dominant and most common species, Anna's hummingbird.Based on the data, I suggest that Aggressive Resource Neglect (ARN) promotes coexistence and results in higher diversity when resources are augmented. When there are more feeders, they are distributed over a larger area. This reduces the ability of a territory-owner to defend these resources. While the territory-owner chases intruders, other individuals gain access to feeding opportunities. When dominant individuals prefer chasing conspecifics (as with Anna's hummingbird), this results in higher diversity.Besides discussing theoretical aspects, I apply this knowledge to conservation. Information on the community ecology enabled me to suggest ecologically-based ways to reconcile the city for native hummingbirds. By adding resources following an ecological protocol, we can promote biodiversity and surround ourselves with native wildlife, such as hummingbirds.

The degree to which biotic interactions influence invasion success may partly depend on the evolutionary relationship between invaders and native species. In particular, since host-use by enemies such as invertebrate herbivores and fungal pathogens tends to be phylogenetically conserved, exotic plants that have close native relatives in the invaded range should be more likely to interact with enemies. In this thesis, I explore this idea using a series of experiments and field surveys at nested taxonomic levels. My results indicate that exotics from multiple plant families experience lower damage if their average phylogenetic distance from locally co-occurring native family members is higher. I then demonstrate that within the Asteraceae, foliar and capitular damage are lower on exotic compared to native species. Both damage types had a relatively large phylogenetic component, but did not decline with phylogenetic distance to native or exotic confamilials. Finally, I show that communities with versus without close relatives are unlikely to differ in resistance to the novel invader, Solidago virgaurea: biotic resistance imposed by competitors, generalist vertebrates, and specialist invertebrates resulted in similar patterns of damage and mortality regardless of the presence of congeneric natives. In some cases, effects of biota were positive: growth of S. virgaurea seedlings in soils collected near congeneric natives was enhanced more than in soils from communities where congenerics were absent. Overall, these results suggest that biotic interactions between exotic and native species can be phylogenetically structured, although trends based on distance measures tend to be weak. In some cases, damage does decline with phylogenetic distance to native species; however this trend is unlikely to be a strong force limiting invasion or structuring plant communities. These results have significant implications for current theories of invasion biology including the "Enemy Release Hypothesis" and "Darwin's Naturalization Hypothesis", as well as for community phylogenetics.